XV] LEPIDOPHLOIOS 107 



edge of the section) which was formed on the outside of the 

 phellogen. The phellogen is a cylinder of actively dividing 

 cells in the outer part of the cortex of the stem, often 

 spoken of as the cork-cambium or cortical meristem, which 

 produces a considerable amount of secondary cortical tissue on 

 its inner face and a much smaller amount towards the stem 

 surface. This delicate cylinder frequently forms a natural line 

 of separation between the outer shell of bark and the rest of 

 the stem. In the specimen before us, the thin-walled cells of 

 the phellogen were ruptured before petrification and the outer 

 shell of bark was thus separated as a hollow cylinder from the 

 rest of the stem : this cylinder was then flattened, the two inner 

 surfaces coming into contact. Fig. 146, D, represents a section 

 of one half of the thickness of the flattened shell. 



This separation of the outer cortex, and its preservation 

 apart from the rest of the stem, is of frequent occurrence in 

 fossil lycopodiaceous stems. The flattened outer cortical shell 

 of a Lepidophloios, specifically identical with that shown in 

 fig. 146, A and D, was erroneously described by Dr C. E. Weiss 

 in 1881 as a large lepidodendroid cone^. 



Fig. 146, B, affords a view of the inner face of the specimen of 

 which the outer surface is seen in fig. 146, A: the surface shown 

 in the lower part of the drawing, on which the boundaries of 

 the cushions are represented by a reticulum, corresponds to 

 the inner edge of the strip of secondary cortical tissue repre- 

 sented by the vertically shaded band in fig. 146, D. 



The shaded surface in fig. 146, B, represents a slightly 

 deeper level in the stem which corresponds to the outer edge of 

 the vertically shaded band of fig. 146, D : the narrow tapered 

 ridges (fig. 146 B) represent the leaf-traces passing through the 

 secondary cortex, and the fine vertical shading indicates the 

 elongated elements of which this strip of secondary cortex is 

 composed. 



In the longitudinal section diagrammatically reproduced in 

 fig. 146, D, cut along the line ab of fig. 146, A, the parenchymatous 

 tissue of the stout cushions has been partially destroyed, as at 

 a; at s is seen the section of a Stigmarian rootlet which has 



1 Seward (90). 



